[PATCH] posix: Do not use WNOHANG in waitpid call for Linux posix_spawn

[Florian Weimer]

On 10/22/2017 10:51 PM, Adhemerval Zanella wrote:
> As shown in some buildbot issues on aarch64 and powerpc, calling
> clone (VFORK) and waitpid (WNOHANG) does not guarantee the child
> is ready to be collected.  This patch changes the call back to 0
> as before fe05e1cb6d64 fix.

I see it on x86-64, too.  It does look like a kernel bug.

> This change can lead to the scenario 4.3 described in the commit,
> where the waitpid call can hang undefinitely on the call.  However
> this is also a very unlikely and also undefinied situation where
> both the caller is trying to terminate a pid before posix_spawn
> returns and the race pid reuse is triggered.  I don't see how to
> correct handle this specific situation within posix_spawn.

Agreed.  I wish we could do better here, but it seems we can't.

Thanks,
Florian